On Cryptography, and in several other online forums, Hadmut Danisch
<[EMAIL PROTECTED]>, a respected German information security analyst,
recently published a harsh critique of one optional feature in the
SID800, one of the newest of the six SecurID authentication tokens --
some with slightly different form-factors, others with additional
security functions -- sold by RSA. It's raised quite a stir, and I'd
like to respond.
A personal authentication token, by classical definition, must be
physical, personal, and difficult to counterfeit. The most popular
implementations in computer security move the calculation of a
pseudo-random authentication code -- a so-called "One-Time Password,"
or OTP-- off an employee's PC and into a hand-held hardware fob,
small enough to be attached to a personal key chain.
RSA's mainstay token, the SID700 SecurID -- millions of which are
used in over 20,000 enterprise installations worldwide, including
many government agencies and financial institutions -- use AES (the
US cryptographic standard) to process Current Time and a 128-bit
token-specific secret to generate and continuously display a series
of 6-8 digit (or alphanumeric) OTP "token-codes" which change every
60-seconds, and remain valid only for a couple of minutes.
In practice, a RSA authentication server can then independently
calculate the token-code that is appearing on a specific SecurID at
this particular moment; compare that against an OTP submitted by a
pre-registered user, and validate a match. RSA, which first
introduced the SecurID in 1987, has always insisted on the necessity
of "two-factor authentication" (2FA), where a remote RSA
authentication server must validate both a SecurID token-code
(evidence of "something held") and a user-memorized PIN or password
("something known.")
A stolen password can be reused indefinitely to masquerade as the
legitimate user, often with the victim wholly unaware. A
token-generated OTP, valid only briefly, is a far more robust
authenticator. With 2FA, if a SecurID is stolen or lost, it still
can't be used to obtain illicit access to protected resources without
the second secret: the user's memorized PIN or password.
The elegant simplicity of the traditional SecurID -- and patents on
the mechanism by which the "drift" in each individual SecurID's
internal clock is tracked by the RSA authentication server -- has
allowed RSA's "time-synched" SecurID to dominate the market niche for
hand-held OTP authentication devices for 20 years.
In a typical installation, anyone seeking to log on to a protected PC
or network, or to access restricted online resources, must manually
type in the OTP currently displayed on the SecurID -- as well as his
memorized PIN or password -- to have his identity and access
privileges validated. Network applications handle the combined
SecurID "pass-code" like any long traditional password. The link
between the user and the RSA infrastructure is often, but not always,
an encrypted VPN channel. That's a local decision. Data exchanges
between the RSA agent and RSA authentication server -- which
typically means between one of the 350-odd "SecurID-aware" network
applications and the RSA Authentication Manager, using RSA's own
protocol -- are always fully encrypted.
Mr. Danisch is an admirer of the classic SecurID (SID700), RSA's
traditional hand-held token. His ire is directed at one of the two
new hybrid SecurID designs that RSA has recently offered in an
attempt to respond to new requirements in the boisterous and
rapidly-evolving market for what's called "strong authentication."
With the nascent prospect of a new billion-dollar market in consumer
authentication for financial services boosted by US federal
regulatory initiatives, RSA announced the SecurID Signing Token, the
SID900. The SecurID Signing Token still has a time-synched OTP, but
RSA added a keypad and a challenge/response function which
successively authenticates the user, the remote server, and a
specific financial transaction, before the transaction (e.g., a funds
transfer) is executed.
On the other side of the market -- where again US laws and federal
regulatory initiatives have boosted demand for internal controls and
more accountability measures in enterprise IT -- RSA has introduced
the SID800, another hybrid SecurID, to meet the requirements of
organizations that want to move into a full public key infrastructure (PKI.)
The SID800 SecurID is a multi-function authentication and
cryptographic device that combines, in a single DPA-resistant token,
the mobility and availability of the classic hand-held SecurID, as
well as a "smart chip" that implements v2.1.1 Java tech (essentially
a "virtual smart card") in a USB format. It looks like a slightly
smaller version of the classic SecurID key fob, with a USB plug
jutting out at one end. It can carry up to seven X.509 digital
certificates for PKI, as well as account information and complex
passwords for up to three Windows accounts. The SID800's lithium
battery allows it to continuously generate and display 60-second
SecurID OTPs for up to five years.
The SID800 "smart chip" has the typical load of standards-compliant
smart card functionality: ANSI X9.31 PRNG, client-side PKI support
including key generation for DES/3DES and 1024-bit RSA Public Key
Cryptography, SHA-1 hashing, and 1024-bit RSA digital signatures.To
access its local cryptographic services (key generation,
authentication, file encryption, digital signatures, etc.) and its
X.509 certificates -- complex resources that require a
circuit-to-circuit connection and interactive data exchanges -- the
SID800 SecurID can be plugged directly into a PC's USB port.
None of these features -- none of the SID800's cryptographic
resources -- were of apparent interest to Mr. Danisch. He ignored
them all when he denounced the SID800 as "vulnerable by design."
The classic SecurID, declared Mr. Danisch on the Cryptography mailing
list, "is a smart device which provides a reasonable level of
security in a very simple and almost foolproof way...."
"It's a pity," he added, "to see it weakened without need..." The
traditional SecurID has the advantages (and disadvantages) of an "air
gap." With no direct circuit connection to the user's PC or client
terminal, it has no direct vulnerability to the various classes of
malicious or larcenous malware which -- Mr. Danisch warns -- can
potentially overwhelm and totally corrupt PCs, and particularly Windows PCs.
What particularly disturbs Mr. D is one option among in the SID800
SecurID features which allows RSA's local client software to poll and
retrieve a single OTP from the token when the SID800 is plugged into
the PC's USB port. Given the potential for malicious malware to
invade and take control of any Windows PC -- malware that can seize
and misuse both the user's PIN and an OTP fresh from the USB bus --
it was irresponsible, Danisch suggests, for RSA to make such a option
available to its customers.
There are actually two versions of the SID800 sold by RSA. In one
version, there is none of the fancy new OTP functionality that
worries Mr. D. In this model, the only way to use the SecurID's OTP
is the old-fashioned way: to read the LCD and type it (and the user's
PIN) at the keyboard.
In the second version of the SID800 -- an option selectable by local
management pre-purchase, and burnt into the token's USB firmware by
RSA -- the user can select a menu in which he instructs the SecurID
to load one OTP token-code directly into the paste buffer, presumably
for immediate use. Since internal access to the SecurID's OTP via the
USB bus makes it a potential target for "malware or intruders on the
computer," claimed Mr. Danisch, "This is weak by design." I beg to
differ. Effective IT security is about an appropriate balance, not
walls of iron or stone.
Can this token-code in the paste buffer be misused? Not likely, even
if it is immediately stolen by malware and immediately used for some
nefarious purpose. A SecurID token-code can only be used once; no
replay is allowed. As a defense against race attacks, the RSA
Authentication Manager will also automatically reject both of two
identical token-codes submitted roughly simultaneously -- even if
both are accompanied by the proper PIN -- and log it for
investigation by the security manager. If the legitimate user can use
the token-code, he effectively preempts any misuse of that OTP by a
hostile party or malware.
Could hostile malware independently execute the menu request for a
new token-code -- essentially instruct a token plugged into the USB
port to produce a new token-code, without the knowledge of the user
-- and then swipe it, directly or from the paste buffer? Could
malware collect the PIN and logon data of any authentication process
with a keyboard logger? Unfortunately, it could. Mr. Danisch raises
a valid concern.
The cryptographic functionality of any smart card -- which typically
includes authentication, encryption, digital signatures, etc. -- can
be initialized and misused by a powerful hostile agent which took
control of the user's PC and snatched the user's password. Just as
-- although Mr. Danisch didn't mention this -- the "virtual smart
card" in the SID800, or any similar UBB device, could be initialized
and misused.
The level of malware penetration that Mr. D presumes could corrupt
the client authentication and cryptographic functions in any
contemporary PKI environment, certainly any Windows-based client-side
SSL. (See: "Keyjacking: the surprising insecurity of client-side
SSL," by Marchesini, Smith, and Zhao at
<http://www.cs.dartmouth.edu/~sws/pubs/msz05.pdf>.)
Mr. Danisch denounces RSA for implementing an optional ease-of-use
feature, just because it effectively reduces the implicit security of
OTP authentication to no more than what is provided by any PKI smart
card environment. Some -- but not necessarily me -- might suggest
that this is carrying an appreciation of the unique and sterling
qualities of the classic SecurID's OTP a bit far.
This has been an ongoing debate within the RSA user community for the
past year, where some of the language used in declaring opinions is
not always as civil or restrained as that used by Mr. Danisch. It is
not yet clear how the market's choices and concerns will affect the
next version of the SID800's firmware, expected later this year --
but it seems unlikely that either of the two SID800 versions will be
removed from RSA's sales list.
In security, ease-of-use (which usually implies internal complexity)
is often the enemy of security. Yet, any enhancement in ease-of-use
which will have little or no impact on overall system security is
something of a Holy Grail for both InfoSec vendors and local IT managers.
Some organizations choose to use SID800 SecurIDs which offer RSA's
"OTP paste" feature, others do not. Those who don't are presumably
acting on the basis of a risk analysis of their environment that
determines that the advantages of enhanced usability do not justify
the risks it entails. Many of those, I presume, have concerns
similar to those of Mr. Danisch.
If the hostile malware can wait and capture the initiation password
off the keyboard, it can ask for anything the password can authorize.
From the SID800. From any smart card. From any application. From any
network resource. This is not a new insight. (Ironically, the
SID800's OTP output to the USB bus is relatively more difficult to
misuse, since it is time-constrained, while stolen smart card
functionality typically is not.)
Obviously, if a hostile enemy can load malware that "owns" your PCs,
untrustworthy user authentication is only the beginning of your problems.
If the enemy "owns" your Windows box today -- or any other computer,
for that matter -- he probably totally controls everything that
passes through it, and all devices connected to it. Although the
firmware in a smart card -- or in USB plugs like the SID800 which
offer "virtual smart cards" -- supposedly won't allow the PC to
directly access the token's internal secrets, a computer under the
control of a hostile party can doubtless gain illicit access to the
cryptographic services provided by those devices.
Assuming imperfect defenses in any given technical context --
certainly true with the current Microsoft Windows OS, the leading
browsers, and the protocols now in use for both secure data transfer
and authentication -- the industry consensus calls for multiple
defensive layers. Where one defensive layer leaves a gap, another
will often overlap to cover it. The logic of such an approach is
based on gritty experience: there is no such thing a perfect security!
Mr. Danisch bemoans -- as do other fretful traditionalists like
myself, including many who work for RSA -- the loss of the "air gap,"
the isolation of the SecurID's OTP generation from the potentially
corrupted PC and network. (A networked device will never be as
transparent as the classic OTP token, where everybody knows exactly
what the SecurID is doing, and can be certain that it is doing no
more than it is expected to do. The elegance of simplicity.)
Others -- including many fretful traditionalists -- celebrate
(despite imperfect implementations, despite many inherently
untrustworthy operational environments) the powerful security
utilities which become available with interactive PKI, which RSA
pioneered with its work on the seminal Public Key Crypto Standards
(PKCS) and the revolutionary RSA public key cipher which is critical
to so much of today's network security services.
The two hardest things to do in computer security are (A) to create a
perfectly secure technical infrastructure, and (B) to second-guess
the CIO, CISO, or local system administrator who has the
responsibility to identify his assets, understand his risks, and
select where and how to balance his investments in usable
functionality and information security.
Since no one today argues that perfect security is attainable,
security mavens like Mr. Danisch (and myself) are forever occupied
with the second task. Yet, as Courtney's First Law -- codified 40
years ago by IBM's Bob Courtney, one of the pioneers in computer
security -- puts it: "Nothing useful can be said about the security
of a mechanism except in the context of a specific application and a
specific environment."
Information security vendors like RSA attempt to respond to the
perceived market requirements, juggling concerns about risk,
liability, and cost against demands for functionality, flexibility,
and accessibility. When relative security is slightly compromised
for a perhaps critical enhancement in ease-of-use, it seems smart to
at least give the buyers the option. That leaves the critical
judgment to the professionals who know their environment, their real
risks, and their people, best.
Lecturing CIOs about the relative importance of security threats --
when they have to get real work done in an imperfect universe -- is
as presumptuous as it is almost surely ill-informed. Hectoring
vendors who respond to demands from their customers for alternative
ways to address security issues -- some admittedly more or less
robust than others -- is far more appropriate. In that sense, debates
that arise when critics like Mr. Danisch forcefully state their case
are useful, even necessary.
It is no secret that Windows and the browsers have design
flaws. Client-side SSL still has some major architectural issues,
particularly in Windows. It is no secret that PC users today need a
safer place -- some sort of restricted input environment,
inaccessible to all but the local user -- by which they can submit
authentication calls to an application over a trusted path. It is no
secret that network protocols require new IETF initiatives to better
secure them against attempts to corrupt them for illicit gain. It is
no secret that simple authentication protocols must today often be
supplemented by some form of mutual authentication, or that
high-value transactions may require supplementary authentication, or
that unusual transactions or access claims may trigger direct
oversight or adaptive authentication requirements.
Simple user authentication, simple web server authentication, simple
client-side SSL, basic PKI, is no longer enough when malware is now
usually the sophisticated product of a criminal enterprise. Forensic
audit logs have never been more important. The good news is that --
thanks to concerns raised by outspoken techies like Hadmut Danisch --
there is public debate and significant developments in all these
areas, and solutions (probably imperfect, but better) are on the horizon.
Suerte,
_Vin
PS. I have been a consultant to RSA for nearly 20 years and my bias
is overt. I beg the indulgence of the List for the length of my comments.
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